This invention relates in general to gas treatment devices and in particular to a new and useful construction for a catalyst converter system in an exhaust line of a liquid fuel operated motor.
The invention relates particularly to an arrangement for holding a catalyst in a housing in the exhaust system of a liquid fuel-operated motor and isolating the catalyst against a bypassing exhaust stream by an at least single-ply, corrugated metal knitting, surrounding the catalyst as a holder, which retains the catalyst in its installation position in the housing and which has at least one segment extending in the lengthwise direction of the holder to accommodate a sealing strip.
There are known arrangements in motor vehicles wherein catalytically coated monoliths are accommodated in a housing in the exhaust line of the motor vehicle motor. The monoliths to be retained are sensitive to impact and must be secured in their installation position Since the object to be retained has a coefficient of thermal expansion different from that of the pipeline or the receiving housing, special difficulties result. In the case of catalytically-coated monoliths for cleaning the exhaust gas in motor vehicles, it has been found advantageous to hold the monoliths by a peripheral knitting. This can be done by a knitting arranged at the front end and encompassing the end face of the object, or by mineral weaves arranged along the periphery and encompassing the end faces of the object (German patent No. 22 13 539). Finally, German AS No. 14 76 507 shows another monolith holder in which the surface of the object is covered with a pore-sealing layer of aluminum silicate, after which the holder proper is formed by a metal corrugated knitting. It is also known from German patent No. 22 13 539 that the retained object can be protected from the flow by arranging one or more radial sealing rings between the holder and the housing or the sealing impressions.
In these familiar devices there is a danger that the retained object may be moved by the pulsating process, changing its position and coming into contact with the parts of the housing, thereby becoming damaged. A second, related difficulty is the isolation of the exhaust gas flowing about the object. This stream must be kept as small as possible, since the gas flowing through the object is cleaned by virtue of flowing through the object, e.g. a catalyst, whereas the stream flowing about it remains untreated and rejoins the exhaust behind the catalyst, thus lowering the efficiency of the purification.
Therefore, an improved arrangement for holding a monolith in a housing in the exhaust line of a motor vehicle was disclosed in German OS No. 35 19 965, according to which the holder for the monoliths comprises a flat element of a compressed tubular metal knitting, having arrow-shaped impressions at a certain angle on either side and enveloping the monolith in at least a single ply, with at least one straight impression parallel to the lengthwise axis of this holder to accommodate a sealing strip. Although this arrangement represents a substantial improvement over the previously known layouts, it still has the serious disadvantages that the sealing strip rests on the compressed knitting and, thus, on a rough surface. Accordingly, under the thermal stress of the operating process, by virtue of the different expansions, the compressed knitting may rub against the sealing strip and by abrasion destroy the latter, resulting in loss of sealing action. Furthermore, the abraded matter escapes in the surrounding flow of exhaust gas, polluting the environment. Obviously, this also entails a reduction in lifetime of the exhaust cleaning system, even though enabling a longer working life of the catalytically active monolith.